hdu 1272 判断所给的图是不是生成树 (并查集)

 1 # include <iostream>
 2 # include <cstdio>
 3 # include <cstring>
 4 # include <algorithm>
 5 # include <cmath>
 6 # include <queue>
 7 # define LL long long
 8 using namespace std ;
 9 
10 const int MAXN=100010;
11 int F[MAXN];
12 bool vis[MAXN] ;
13 int save[MAXN] ;
14 bool flag ;
15 int find(int x)
16 {
17     while(x!=F[x])
18         x=F[x];
19      return x;
20 }
21 void bing(int u,int v)
22 {
23     int t1=find(u);
24     int t2=find(v);
25     if(t1!=t2) F[t1]=t2;
26     else flag = 1 ; //有重边
27 }
28 int main()
29 {
30     //freopen("in.txt","r",stdin) ;
31     int u , v ;
32     while(scanf("%d %d" , &u , &v) != EOF)
33     {
34         if (u == -1 && v == -1)
35             break ;
36         if (u == 0 && v == 0)
37         {
38             printf("Yes\n") ;
39             continue ;
40         }
41          int i ;
42          for(i=1;i<MAXN;i++)
43          {
44              F[i]=i;
45          }
46         memset(vis , 0 , sizeof(vis)) ;
47         F[u] = v ;
48         int l = 0 ;
49         flag = 0 ;
50         if (!vis[u])
51         {
52             vis[u] = 1 ;
53             save[l++] = u ;
54         }
55         if (!vis[v])
56         {
57             vis[v] = 1 ;
58             save[l++] = v ;
59         }
60         while(scanf("%d %d" , &u , &v))
61         {
62             if (u == 0 && v == 0)
63                break ;
64             if (flag)
65                 continue ;
66             if (!vis[u])
67         {
68             vis[u] = 1 ;
69             save[l++] = u ;
70         }
71             if (!vis[v])
72         {
73             vis[v] = 1 ;
74             save[l++] = v ;
75         }
76             bing(u,v) ;
77         }
78         int res = 0 ; //连通分量
79         for (i = 0 ; i < l ; i++)
80             if (F[save[i]] == save[i])
81                 res++ ;
82         if (res >= 2 || flag == 1)
83             printf("No\n") ;
84         else
85             printf("Yes\n") ;
86     }
87     return 0;
88 }